ROP

[Shadrach]

6 hours ago, jaylw314 said:

It's hard to imagine that there's realistically much more efficiency to be had.  The IO-360 at 130hp at Mooney's POH "best economy" of 25 ROP uses about 9.3 gph.  By my calculations, that's a BSFC of 0.43.  I'm guessing here, but LOP might bring it down to about 0.42 or so.

In contrast, the 200hp Ford EcoBoost has a BSFC of 0.40.  Granted, that's comparing apples to oranges, but it's hard to see a gasoline engine gaining significant efficiency moving forwards.  LOP is a low-risk, low-effort, and low-cost method for improving efficiency.  OTOH, investing money in high-cost, high-risk and high-effort methods like electronic ignition are unlikely to be worthwhile for most people or manufacturers

Easy to run the approximate numbers. Though more of a thought exercise given we’re converting gallons to pounds using a 6lbs.  All other things being equal, At 65% the calculations work out to:

ROP 9.3GPH (BSFC .429) 

LOP 8.6GPG (BSFC ..399)

If you run that way for 1300 of your 2000hr of TBO you save a measly 910 gallons of fuel or about $5500 at todays prices. 

The above calculations are pretty simple and do not account for more detailed variables but the comparison is valid.

[Shadrach]

54 minutes ago, A64Pilot said:

I deleted the rest of that as I read the Gami article about it 20 years ago, but was unaware the Engineer could advance timing.

‘But you need to read the article where the Pax river test pilot ran a series of tests running LOP etc on a fuel injected 200 HP lycoming in his RV-8  and had electronic ignition that allowed him to change timing. It’s in one of these threads.

His take was that it didn’t make as much difference in fuel consumption, that climbing just a few thousand feet would do better.

So I guess we should take this Naval Test Pilot and group him with the engine manufacturers, that is they don’t know what they are all talking about.

There are gains, but they aren’t nearly what people want to believe

He was flying a high compression IO360 in an 1,100lb sport plane.  His take was that climbing an additional 4000 feet would yield the same performance. No big deal for him, his ROC through 20,000 would likely be enviable by most NA Mooneys at half that altitude. Going from 12K to 16K, in a NA Mooney, in August is doable, but is not comparable to modified RV.  

Another interesting part but not really mentioned part of the article was the difference in Performance between 21° and 25° of advance. He stated that his engine data plate is stamped for 25°.  All of his data is at 21° or more. He did not bother to record LOP date below 25° but ROP just 4° of advance made a noticeable difference in speed.  This was a good write up but it would have been better if he had attempted an all "other things being equal" approach where possible to each setting.

[A64Pilot]

1 hour ago, Shadrach said:

Easy to run the approximate numbers. Though more of a thought exercise given were converting gallons to pounds using a 6lbs.  All other things being equal, At 65% the calculations work out to:

ROP 9.3GPH (BSFC .429) 

LOP 8.6GPG (BSFC ..399)

If you run that way for 1300 of your 2000hr of TBO you save a measly 910 gallons of fuel or about $5500 at todays prices. 

The above calculations are pretty simple and do not account for more detailed variables but the comparison is valid.

How ROP are you in your ROP example?

Two things are issues, first the Gami guys always say simply increase MP to recover lost speed, well at the altitudes I cruise at that’s not possible, at 7,500 ft all there is, is 22” of manifold pressure, less if higher of course, but at 7,500 there is no simply increase MP. When traveling the throttle is opened on takeoff and stays there until the descent to land.

Then there is the small issue of the speed difference between your two examples, from my testing years ago if I ran at Lycomings suggested 50 ROP or peak and -25 LOP, and set identical speeds, my fuel burn was less than 1/2 gl difference in a 540, so I’d guess may 1/4 gl difference in my 360. I don’t have the multi point calibrated instrumentation now that I had then, and frankly the desire to retest in my J model.

In order for LOP and ROP to be compared be sure your not excessively rich and speeds are identical.

I’m not saying don’t run LOP, I do most flights, but if I’m traveling the loss in speed at altitude may not be worth it. I’m not talking flight levels and I don’t think the guy who did that test was either, but altitude and speed are the way to save fuel. Climb and run peak, most won’t reduce power if for example all you can get is 19” which is about 10,000, but fuel burn will be down but speed pretty good due to less air resistance. Less than it will be lower at the same speed LOP, that was his point, and he was able to turn ignition timing all the way to 40 deg if memory is correct.

I run LOP most flights as they are short go out to eat types of flights below 3,000 MSL, and I’m not in a hurry. LOP makes the most sense then 

[jaylw314]

2 hours ago, A64Pilot said:

How ROP are you in your ROP example?

That was based on the Mooney POH "best economy" of 25 ROP at 2500 RPM and 65% power

Edited May 24, 2022 by jaylw314

[jaylw314]

4 hours ago, Shadrach said:

Easy to run the approximate numbers. Though more of a thought exercise given were converting gallons to pounds using a 6lbs.  All other things being equal, At 65% the calculations work out to:

ROP 9.3GPH (BSFC .429) 

LOP 8.6GPG (BSFC ..399)

If you run that way for 1300 of your 2000hr of TBO you save a measly 910 gallons of fuel or about $5500 at todays prices. 

The above calculations are pretty simple and do not account for more detailed variables but the comparison is valid.

Thanks, I didn't have time to find and crunch all the numbers  

With fuel efficiency, people tend to look at the wrong values.  In cars, it's the absolute reduction in fuel consumed per year that is the most important economic and environmental factor.  Getting another car with twice the mpg is less important than switching from an SUV to any car.

In planes, IMO it's the amount of reserve fuel that you land with, since it's a safety factor.  The difference between 8.6 and 9.3 gph might be significant for a long trip in terms of an extra 3-4 gallons, but usually not since we want to land with at least 9-10 gallons.  If there is something out there that will reduce our fuel use from 8.6 to 8.4 gph, that will make even less of a difference.  Conversely, flying slower will produce a far more substantial improvement in reserve on landing.

[Shadrach]

18 minutes ago, jaylw314 said:

Thanks, I didn't have time to find and crunch all the numbers  

With fuel efficiency, people tend to look at the wrong values.  In cars, it's the absolute reduction in fuel consumed per year that is the most important economic and environmental factor.  Getting another car with twice the mpg is less important than switching from an SUV to any car.

In planes, IMO it's the amount of reserve fuel that you land with, since it's a safety factor.  The difference between 8.6 and 9.3 gph might be significant for a long trip in terms of an extra 3-4 gallons, but usually not since we want to land with at least 9-10 gallons.  If there is something out there that will reduce our fuel use from 8.6 to 8.4 gph, that will make even less of a difference.  Conversely, flying slower will produce a far more substantial improvement in reserve on landing.

I'm not flying at 65% power unless dictated by altitude.  I fly as close to peak EGT as possible with good cooling margins which mean LOP when cruising down low to avoid winds. Peak above DAs of about 5K switching to slightly ROP above 10K and 100° in the teens. Rather than slow down, I will always choose higher if possible.

[Shadrach]

16 hours ago, A64Pilot said:

How ROP are you in your ROP example?

I'm using @jaylw314's 9.3GPH @ 65% (130hp) at 25° ROP example. 65% (130hp) @ 100° ROP in my POH is ~9.7GPH.  65% (130HP) when LOP is ~8.6GPH in the flat part of the BSFC curve.

Two things are issues, first the Gami guys always say simply increase MP to recover lost speed, well at the altitudes I cruise at that’s not possible, at 7,500 ft all there is, is 22” of manifold pressure, less if higher of course, but at 7,500 there is no simply increase MP. When traveling the throttle is opened on takeoff and stays there until the descent to land.

GAMI/APS guys say that but they are pretty clear they are not comparing apples to apples power levels.  If they were, they would not mention the speed penalty.  They do this to help new pilots understand a simple way to lean their NA aircraft.  However, They also talk about apples to apples horsepower comparisons especially with TN'd Bonanzas.  The thing is, you don't need a Turbo to run apples to apples HP comparisons at lower altitudes. It is entirely feasible to run an engine LOP at 65% at 4500', you can also run ROP at 65% horsepower at that altitude. 130HP is 130HP is 130HP, the airplane does not care how you make it. The IAS will be the same, the MP and fuel flow will not.

Then there is the small issue of the speed difference between your two examples, from my testing years ago if I ran at Lycomings suggested 50 ROP or peak and -25 LOP, and set identical speeds, my fuel burn was less than 1/2 gl difference in a 540, so I’d guess may 1/4 gl difference in my 360. I don’t have the multi point calibrated instrumentation now that I had then, and frankly the desire to retest in my J model.

It's not an issue in my example. As I said above their is no difference in speed between 65% hp 10 LOP and 65% hp 100 ROP.  The Manifold pressure will be higher LOP and the FF and CHTs less but the speed will be the same.

65% power is achievable with an NA engine on either side of peak at some altitudes. If one wishes to compare apples to apples, one must do so at those altitudes. You are conflating the operational limitations of flying an NA engine at altitude with the comparison same HP to same HP. You're not the first to do this and you won't be the last...  It might help to imagine a Turbo engine which can develop enough MP to run 70% ROP or LOP.  I have attached a photo from GAMI's website of an Aerostar running both engines at the same power and RPM. Left is ROP and Right is LOP.  MP, FF and CHTs are very different. The ball is not visible in the picture but I have no doubt that it was perfectly centered.

In order for LOP and ROP to be compared be sure your not excessively rich and speeds are identical.

I use book power settings when making comparisons. That's usually 100ROP In the winter time we can have DAs of 1000' at 4500msl. There are no book settings for the MP at wide open throttle and 2500RPM other than full rich.  I have three choices.  Leave the knobs forward and puke 16gph or more through the engine. Throttle back and lean for 75% @ 100ROP or pull mixture to LOP.  Under some conditions, I can run faster LOP than throttled back to 75% 100ROP. Why because there is adequate MP available to run greater than 75% while LOP. The only trouble is keeping CHTs above 300 when LOP at those airspeeds with OATs in the teens.

I’m not saying don’t run LOP, I do most flights, but if I’m traveling the loss in speed at altitude may not be worth it. I’m not talking flight levels and I don’t think the guy who did that test was either, but altitude and speed are the way to save fuel. Climb and run peak, most won’t reduce power if for example all you can get is 19” which is about 10,000, but fuel burn will be down but speed pretty good due to less air resistance. Less than it will be lower at the same speed LOP, that was his point, and he was able to turn ignition timing all the way to 40 deg if memory is correct.

I run LOP most flights as they are short go out to eat types of flights below 3,000 MSL, and I’m not in a hurry. LOP makes the most sense then.

I too run LOP down low. The difference between us is that I am 15 to 20kts faster and burning a little more gas.  Even this time of year CHTs are all still well under 350, some considerable less. 

Replies above in Italicized bold.

From my with attachments from my iPhone. The website made me convert a 63 KB screenshot into a PDF 602KB to upload. That seems stupid so here’s a link to the Aero star article on GAMI’s website.

https://gami.com/articles/baconsbonus.php

Edit: I was able to upload the pic. IO-540-S1A5 same power, side by side.

 

[A64Pilot]

13 hours ago, jaylw314 said:

That was based on the Mooney POH "best economy" of 25 ROP at 2500 RPM and 65% power

I didn’t mean your numbers but Shadrach. I’m not saying he is, but often when people compare how much LOP saves they don’t compare to best economy number or peak, they use best power.

Then the obvious, if your at 2500 RPM and can only make 65% at 25 ROP, unless you have the throttle pulled back, your not going to make 65% LOP, maybe at 2700 but that brings inefficiencies and more noise and wear.

If however you do have the throttle pulled back, you should lower RPM and run full throttle for several reasons, higher RPM brings increased internal engine friction, the prop is less efficient as higher RPM brings higher drag, and of course reduced throttle is less efficient due to pumping losses, that is there is a vacuum in the intake manifold and the engine has to work against this vacuum.

None of those will bring big reductions in fuel consumption, but a percent or two here and there add up. Won’t be a big difference though.

[N201MKTurbo]

I limit my power by CHT. I give it as much as I can without exceeding 380 CHT. I can get more airspeed LOP than ROP at 380 degrees. About 4 KTS. ROP is about 11.5 GPH, LOP is about 9.5 GPH. This is at 2400 RPM and 27 in MP LOP or about 25 in ROP.

While ROP, I use throttle to control power, while LOP I use mixture to control power.

Edited May 25, 2022 by N201MKTurbo

[N231BN]

I limit my power by CHT. I give it as much as I can without exceeding 380 CHT. I can get more airspeed LOP than ROP at 380 degrees. About 4 KTS. ROP is about 11.5 GPH, LOP is about 9.5 GPH. This is at 2400 RPM and 27 in MP LOP or about 25 in ROP.
While ROP, I use throttle to control power, while LOP I use mixture to control power.

Same here with my 231. Same speed 65% ROP or LOP, 11.7 GPH vs 10. It's great having the flexibility of a turbo, especially since I don't have to pay anyone to work on it:)

[T. Peterson]

On 5/19/2022 at 3:08 PM, Shadrach said:

Understood, but you should know that “the line” (the setting) that is most abusive to a cylinder is ~40°ROP.  There are plenty of ways to get there if you don’t know what you’re doing or have just a single cylinder monitor.

Why is 40 degrees ROP abusive to a cylinder? Is it because generally speaking that is where the most heat is generated, or is it something else? As you can tell, I am a rookie, but trying to sort all this out.

Torrey

[PT20J]

54 minutes ago, T. Peterson said:

Why is 40 degrees ROP abusive to a cylinder? Is it because generally speaking that is where the most heat is generated, or is it something else? As you can tell, I am a rookie, but trying to sort all this out.

Torrey

It's the mixture that produces the highest CHT. Relative to the best power mixture, the power is lower, but the CHT is higher. It's only "abusive" at high power settings where the CHTs get too high. It is probably the mixture strength for the lowest detonation margin (although that is not to say that it will cause detonation). Look back a few posts at the Lycoming chart that @Shadrach posted that shows the relationship between EGT, power, BSFC and CHT and all this will be clearer

[Shadrach]

6 hours ago, T. Peterson said:

Why is 40 degrees ROP abusive to a cylinder? Is it because generally speaking that is where the most heat is generated, or is it something else? As you can tell, I am a rookie, but trying to sort all this out.

Torrey

I should have been more clear. It’s a perfectly useable setting but it is about the hottest mixture setting there is with regard to CHT. Keep in mind the Lycoming chart is a conceptually accurate depiction of the relationships, not a precise illustration of CHT change. I would not count on the 45°F (7.5°C) drop in CHT from 40ROP to peak to be exact, but it’s close enough. 

[A64Pilot]

We all want what is the best x for everything, best oil pressure, best RPM etc. It’s human nature for us to want to operate at the best conditions.

Unfortunately at least for mixture there is no best, there are multiple best. Best changes with power setting, LOP is entirely correct and best if you can run it and make enough power doing so, but aren’t trying to make high power, peak is a correct mix at times as well as 50 ROP, 100 ROP and full rich.

Its complicated, but it can be fun optimizing economy, learning enough to do so, but it can be harmful if you get it wrong easily costing way more than you will ever save, and can even be unsafe.

If you want to keep things KISS and want to ensure you won’t hurt anything, operate IAW the POH, you will burn a little more fuel doing so, but will most often be cruising faster and you will be sure to not hurt anything.

Mooney and Lycoming / Continental aren’t stupid they know how the engines can be operated but they give you procedures that both give good performance and a good safety margin. Follow their procedures and you won’t hurt anything

If you want to play mixture games outside of the POH be careful, it’s entirely possible to damage the engine. However if you play the games at low power, less than 65% you can’t hurt the motor, and Lycoming says a motor run at or less than 65% will last longer, and if your doing it to save fuel, running lower power will likely save more fuel than LOP, but together you can save even more.

If your a 200 HP Lycoming it’s easy to know if your less than 65%, if your LOP and burning less than 8 GPH, your under 65% and therefore safe. It really is that simple. I’m sure there is a number for the 550 but I don’t know what it is.

‘The actual safety number is higher than 8 GPH, but I like safety margins

Except for a trip taking a little longer I can’t see a downside to operating at 65% or less, and if the trip is of any significant  distance your probably at an altitude where you can’t make more than 65% anyway. Due to lower air density altitude also saves fuel and you go faster to a point. N/A motor.

Edited May 27, 2022 by A64Pilot

[Cruiser]

1 hour ago, Shadrach said:

I should have been more clear. It’s a perfectly useable setting but it is about the hottest mixture setting there is with regard to CHT. Keep in mind the Lycoming chart is a conceptually accurate depiction of the relationships, not a precise illustration of CHT change. I would not count on the 45°F (7.5°C) drop in CHT from 40ROP to peak to be exact, but it’s close enough. 

the Lycoming chart (Figure 3-1) is used a lot to visually describe ROP/LOP. The graph is deceptive in that the scale are not the same for CHT. Why Lycoming did this was really a disservice to the understanding of EGT/CHT relationships in a visual sense. EGT is graphed in °F and CHT is graphed in °C. That relationship is critical to understanding the 'red box' and the chart really does a very poor job of showing it. The CHT curve is reduce by a factor of 1.8 degrees for every 1.0 degrees of EGT change.  If you graph the CHT in °F there will be a huge spike upward for the CHT that would stand out on the graph like the sore thumb it is in the redbox. 

[Cruiser]

23 minutes ago, A64Pilot said:

snip...

If your a 200 HP Lycoming it’s easy to know if your less than 65%, if your LOP and burning less than 8 GPH, your under 65% and therefore safe. It really is that simple. I’m sure there is a number for the 550 but I don’t know what it is.

... snip

for the Continental IO-550G that FF is 13.5 gph. 

[Shadrach]

7 hours ago, Cruiser said:

the Lycoming chart (Figure 3-1) is used a lot to visually describe ROP/LOP. The graph is deceptive in that the scale are not the same for CHT. Why Lycoming did this was really a disservice to the understanding of EGT/CHT relationships in a visual sense. EGT is graphed in °F and CHT is graphed in °C. That relationship is critical to understanding the 'red box' and the chart really does a very poor job of showing it. The CHT curve is reduce by a factor of 1.8 degrees for every 1.0 degrees of EGT change.  If you graph the CHT in °F there will be a huge spike upward for the CHT that would stand out on the graph like the sore thumb it is in the redbox. 

I totally agree that the visual representation is much more dramatic when like units of measure are used. I think Lycoming did this for aesthetic reasons and also to make the chart more compact and readable. I think one of the greatest sins of the chart is that it suggests CHT movement is linear on each side of peak. Anyone with real world experience looking at the numbers knows that isn’t actually the case.  

[Fly Boomer]

9 hours ago, T. Peterson said:

As you can tell, I am a rookie, but trying to sort all this out.

Don't know if you like to read sometimes tedious technical stuff, but this Mike Busch article is the best condensation of the APS course (If that's even possible) I can think of.

Savvy Aviator 59 - EGT, CHT, and Leaning.pdf

[Shadrach]

If I use the cruise data in my POH. Any power setting up to 74.9% is given at 100° ROP, any setting above that is full rich. The airplane was delivered with gauges for CHT and EGT on #3.  Some of the POH power/mixture settings are not very conservative when it comes to engine health or efficiency but are instead geared towards extracting max speed from an efficient airframe for marketing purposes . Those settings will still yield CHT’s below the factory CHT redline of 475° but likely at the top of or above the “green arc”  operating range of 300° - 400° CHT (if everything is functioning properly). With the factory single probe gauges, what you don’t know may not hurt you, these engines are pretty robust.

That being said, I would submit that the optimal setting is always the one that yields the highest power at the lowest BSFC while maintaining healthy CHTs. My POH does a lousy job of depicting those settings, which differ based on altitude and OAT.  

The whole point of understanding and applying these concepts to a well instrumented engine is to get away from single recipe “cookbook“ settings. Small tweaks of the mixture, throttle or prop control can have a dramatic effect on CHT and fuel flow with minimal impact on speed.

One advantage of understanding and applying these concepts is being able to take an optimal course of action when something is not operating as it should. Yet another advantage is being able to precisely describe the symptoms to a maintenance professional that wasn’t present during the event (though it may be challenging to find one that understands what you’re saying). 

I once picked up my airplane from maintenance and and recognize the elevated number for CHT on climb out. The occurred to me almost immediately that whomever had installed my top cowl did not properly face the baffle seal forward and a great deal of air was leaking into the accessory compartment rather than removing heat from the rear left cylinder. I should have caught it during preflight, but I’m glad I had a second chanc. I lowered the nose and RTB. Don’t know when I’d have caught it with out the monitor.  I am the only ECU my engine has. I feel much safer being able to see that things are operating normally in real time. I would not want to go back to faith based operations.

You can learn to cook or you can just follow a recipe.  It’s harder to learn to cook initially, but once you’ve learned it’s much easier to get the best results out of the ingredients on hand.

[PT20J]

1 hour ago, Fly Boomer said:

Don't know if you like to read sometimes tedious technical stuff, but this Mike Busch article is the best condensation of the APS course (If that's even possible) I can think of.

Savvy Aviator 59 - EGT, CHT, and Leaning.pdf 105.02 kB · 8 downloads

Just to show that there are differences of opinion about this, here is an article written by John Deakin objecting to Mike’s approach. Personally, I agree with Mike’s simpler approach, but keep in mind that one of Mike’s keys to success is to run at low power (65% or less). Deakin used to like to run LOP at higher power settings.

https://www.avweb.com/features/pelicans-perch-84-dont-set-mixture-with-cht/

 

[PT20J]

7 hours ago, Cruiser said:

the Lycoming chart (Figure 3-1) is used a lot to visually describe ROP/LOP. The graph is deceptive in that the scale are not the same for CHT. Why Lycoming did this was really a disservice to the understanding of EGT/CHT relationships in a visual sense. EGT is graphed in °F and CHT is graphed in °C. That relationship is critical to understanding the 'red box' and the chart really does a very poor job of showing it. The CHT curve is reduce by a factor of 1.8 degrees for every 1.0 degrees of EGT change.  If you graph the CHT in °F there will be a huge spike upward for the CHT that would stand out on the graph like the sore thumb it is in the redbox. 

I don't think it's quite that dramatic for a real engine. Below is a curve from a 1990 Continental Maintenance and Operator's Manual for an IO-550G. The document does not specify how the data was obtained, but it is a good bet that it was in a test cell with calibrated instrumentation using a test club and very good cooling airflow. There are a few interesting things to note. 

1) Note how high the CHTs are ROP. This is why above 65% power Continental wants you to be full rich (and APS says to be careful about being too rich when LOP). This is the origin of the red box. I believe that most of the data in the APS course (at least in 2007 when I attended) comes from big bore Continental engines. Other engines are more robust. A Lycoming IO-360 will run quite a bit cooler in my experience.

2) Note that the EGT peak is not very sharp. Without knowing where the measurement was taken it is hard to know for sure why, but it probably is due to poor mixture balance between cylinders (this was before Continental started shipping engines with GAMI-style balanced injector nozzles). A theoretically perfect engine would have a sharp peak with constant slope on each side. Even a single cylinder real engine will have some rounding due to cycle-to-cycle variation in combustion.

3) Note that the minimum BSFC is about 0.375 pph/hp or 72 pph for about 215 bhp. Using the average of 6 lbm/gal for avgas, this is 12 gph for 215 bhp or a multiple of 17.9 * fuel flow which is not the "typical" number of 15 most people use for a 8.5:1 compression ratio. So, there is no use trying to be overly precise in calculating this number for different compression ratios since it is an approximation in the first place. (The APS calculation assumes a 0.39 pph/hp and assumes that the density of 100LL is 5.85 lbm/gal. The actual density of gasoline depends on temperature and how much of the volatile compounds have evaporated. Generally, 6 lbm/gal is probably closer to what's actually in your tanks). WEB_Aviation_Gasoline_110LL.pdf

Skip

Edited May 27, 2022 by PT20J
Added Avgas spec.

[T. Peterson]

8 hours ago, Shadrach said:

If I use the cruise data in my POH. Any power setting up to 74.9% is given at 100° ROP, any setting above that is full rich. The airplane was delivered with gauges for CHT and EGT on #3.  Some of the POH power/mixture settings are not very conservative when it comes to engine health or efficiency but are instead geared towards extracting max speed from an efficient airframe for marketing purposes . Those settings will still yield CHT’s below the factory CHT redline of 475° but likely at the top of or above the “green arc”  operating range of 300° - 400° CHT (if everything is functioning properly). With the factory single probe gauges, what you don’t know may not hurt you, these engines are pretty robust.

That being said, I would submit that the optimal setting is always the one that yields the highest power at the lowest BSFC while maintaining healthy CHTs. My POH does a lousy job of depicting those settings, which differ based on altitude and OAT.  

The whole point of understanding and applying these concepts to a well instrumented engine is to get away from single recipe “cookbook“ settings. Small tweaks of the mixture, throttle or prop control can have a dramatic effect on CHT and fuel flow with minimal impact on speed.

One advantage of understanding and applying these concepts is being able to take an optimal course of action when something is not operating as it should. Yet another advantage is being able to precisely describe the symptoms to a maintenance professional that wasn’t present during the event (though it may be challenging to find one that understands what you’re saying). 

I once picked up my airplane from maintenance and and recognize the elevated number for CHT on climb out. The occurred to me almost immediately that whomever had installed my top cowl did not properly face the baffle seal forward and a great deal of air was leaking into the accessory compartment rather than removing heat from the rear left cylinder. I should have caught it during preflight, but I’m glad I had a second chanc. I lowered the nose and RTB. Don’t know when I’d have caught it with out the monitor.  I am the only ECU my engine has. I feel much safer being able to see that things are operating normally in real time. I would not want to go back to faith based operations.

You can learn to cook or you can just follow a recipe.  It’s harder to learn to cook initially, but once you’ve learned it’s much easier to get the best results out of the ingredients on hand.

That last paragraph is a great analogy!!

[A64Pilot]

The reason CHT isn’t linear on both sides of peak is because HP output isn’t linear, you lose much more HP per temp when LOP, that’s why we don’t often run 100 LOP, I can but power is so low I can’t stay in the air. CHT and power are pretty closely related until we get way outside of mixture, meaning for example full rich will cool you down significantly but lose only a bit of power

But you were right about both factory’s picking power settings that gave high power and high speeds. At normal cruise altitudes an NA airplane ROP is faster because you can’t make as much power LOP, and it’s my belief Lycoming didn’t want to publish cruise charts that had their engines not making good power

[PT20J]

It's a rare engine that will run well 100F LOP at any reasonable power. As you lean past about 50F, the cycle-to-cycle combustion variation becomes more pronounced as the mixture weakens and when you get too lean the engine runs rough and the power drops so much that the BSFC starts getting worse instead of better. Note that the BSFC curve in the Continental data bottoms out and then begins rising as the mixture is further weakened.

[A64Pilot]

28 minutes ago, PT20J said:

It's a rare engine that will run well 100F LOP at any reasonable power. As you lean past about 50F, the cycle-to-cycle combustion variation becomes more pronounced as the mixture weakens and when you get too lean the engine runs rough and the power drops so much that the BSFC starts getting worse instead of better. Note that the BSFC curve in the Continental data bottoms out and then begins rising as the mixture is further weakened.

Understood, but she will run smoothly 75c LOP at 22 squared 6.5 GPH. That’s in excess of 100 LOP

CHT drops so much LOP because power does, Once rich of best power you don’t have near the power drop per CHT drop that you do LOP, or we wouldn’t take off full rich.

If you could make as much power LOP as you can ROP, then why ever be  ROP?